In recent years, inkjet recording apparatuses that form images by an inkjet recording system are widely used as image forming apparatuses since high-definition image qualities that are comparable to those of silver halide photographs can be obtained due to rapid advances in recording technologies.
In such inkjet recording apparatuses, improvement of an image forming velocity is strongly desired. However, in some cases when an image is formed at a high-speed in an inkjet recording apparatus, a recording medium such as paper bearing an ink passes through an ejection roller and is ejected before the ink has penetrated into the recording medium, and the ink adheres to the ejection roller (offset). In such cases, image defect easily occurs on the formed image. In order to suppress the occurrence of offset, decreasing of the amount of the ejected ink is considered, but in such case, it is difficult to form an image having a sufficient density.
In order to suppress the occurrence of offset, it is also effective to increase the penetrability of an ink into a recording medium. As an ink for an inkjet recording apparatus which is excellent in penetrability into a recording medium and can form a fine image, for example, an aqueous ink including a colorant that is dispersed or dissolved in water, water and a wetting agent, and further including 2-ethyl-1,3-hexanediol is exemplified.
In the above-mentioned ink, 2-ethyl-1,3-hexanediol is used as a component for improving the penetrability of the ink into a recording medium. However, in the above-mentioned ink, in some cases when the content of the 2-ethyl-1,3-hexanediol is small, the penetrability of the ink into a recording medium cannot be enhanced sufficiently, and pollution of the recording medium by offset may be caused. Furthermore, in the above-mentioned ink, in the case when the content of the 2-ethyl-1,3-hexanediol is high, the penetrability of the ink into a recording medium is too high, which leads to a problem that the colorant penetrates into the inside of the recording medium together with the liquid components included in the ink, and thus a formed image has a lower image density than a suitable value.
Furthermore, in the above-mentioned ink, the characteristics of the ink such as thickening are readily changed depending on the kind and amount of the wetting agent, when an image is formed after ejection of the ink from a recording head has been stopped for a while. In this case, the ejection of ink droplets from the recording head may readily become unstable, and image turbulence may readily occur on a formed image. Furthermore, the above-mentioned ink has a problem that, in the case when a recording head in which the ink is filled has been left for a long period, the wetting agent may be solidified in the recording head or significant thickening of the ink may be caused depending on the kind of the wetting agent, thereby the state of ejection of the ink droplets cannot be recovered to the state before the leaving by recovery operations in which purging and wiping are conducted against the recording head.